This section introduces aspects that may be helpful to facilitate a better understanding of the inventions. Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art. Any techniques or schemes described herein as existing or possible are presented as background for the present invention, but no admission is made thereby that these techniques and schemes were heretofore commercialized, or known to others besides the inventors.
The data rate of serial optical interfaces continues to increase and needs to increase to satisfy capacity requirements in the network. High-speed electrical interfaces are required to keep pace with the progress but the test and measurement instrument investments required to keep pace with high-speed systems research and development rise dramatically as well. Optical techniques combined with digital signal processing can provide lower cost alternatives. Today, the highest bandwidth for a commercially available CMOS analog-to-digital converter is approximately 30 GHz and samples at approximately 90 GS/s. On the other hand commercial electrical components are available to build coherent transponder prototypes between 72 and 100 Gbaud, thus requiring at least 50 GHz of bandwidth and 160 GS/s at the receive side ADC. Ultra-high bandwidth ADCs for coherent laboratory experiments are provided by real-time oscilloscopes. Oscilloscope vendors apply digital techniques to provide up to 100 GHz bandwidth and 240 GS/s from lower speed front end electronics and these specification are expected to progress to higher speeds and ultimately very high costs.